Editing Photodiode (section)

==Photodiode array==
[[File:Photodiode array chip.jpg|thumb|150px|right|A one-dimensional photodiode array chip with more than 200 diodes in the line across the center]]
[[File:Optical mouse chip detail.png|thumb|150px|right|A two-dimensional photodiode array of only 4 × 4 pixels occupies the left side of the first [[optical mouse]] sensor chip, c. 1982.]]

A one-dimensional array of hundreds or thousands of photodiodes can be used as a position [[sensor]], for example as part of an angle sensor.<ref>
{{cite book
 | title = Precision Nanometrology: Sensors and Measuring Systems for Nanomanufacturing
 | author = Gao, Wei 
 | publisher = Springer
 | year = 2010
 | isbn = 978-1-84996-253-7
 | pages = 15–16
 | url = https://books.google.com/books?id=N0ys_sSxD60C&pg=PA15
}}</ref>  A two-dimensional array is used in image sensors and [[optical mouse|optical mice]].

In some applications, photodiode arrays allow for high-speed parallel readout, as opposed to integrating scanning electronics as in a [[charge-coupled device]] (CCD) or [[CMOS sensor]].  The optical mouse chip shown in the photo has parallel (not multiplexed) access to all 16 photodiodes in its 4 × 4 array.

===Passive-pixel image sensor===
The [[passive-pixel sensor]] (PPS) is a type of photodiode array. It was the precursor to the [[active-pixel sensor]] (APS).<ref name="Fossum2014">{{cite journal |last1=Fossum |first1=Eric R. |author1-link=Eric Fossum |last2=Hondongwa |first2=D. B. |title=A Review of the Pinned Photodiode for CCD and CMOS Image Sensors |journal=IEEE Journal of the Electron Devices Society |date=2014 |volume=2 |issue=3 |pages=33–43 |doi=10.1109/JEDS.2014.2306412 |doi-access=free }}</ref> A passive-pixel sensor consists of passive pixels which are read out without [[amplifier|amplification]], with each pixel consisting of a photodiode and a [[MOSFET]] switch.<ref name="Kozlowski">{{cite journal |last1=Kozlowski |first1=L. J. |last2=Luo |first2=J. |last3=Kleinhans |first3=W. E. |last4=Liu |first4=T. |editor-first1=Bedabrata |editor-first2=Terrence S. |editor-last1=Pain |editor-last2=Lomheim |title=Comparison of passive and active pixel schemes for CMOS visible imagers |journal=Infrared Readout Electronics IV |date=14 September 1998 |volume=3360 |pages=101–110 |doi=10.1117/12.584474 |url=https://www.researchgate.net/publication/268189518 |publisher=International Society for Optics and Photonics|bibcode=1998SPIE.3360..101K |s2cid=123351913 }}</ref> In a photodiode array, pixels contain a [[p–n junction]], integrated [[capacitor]], and MOSFETs as selection [[transistors]]. A photodiode array was proposed by G. Weckler in 1968, predating the CCD.<ref name=fossum93>{{cite book |last1=Fossum |first1=Eric R. |chapter=Active pixel sensors: Are CCDS dinosaurs? |author1-link=Eric Fossum |title=Charge-Coupled Devices and Solid State Optical Sensors III |journal=SPIE Proceedings Vol. 1900: Charge-Coupled Devices and Solid State Optical Sensors III |volume=1900 |date=12 July 1993 |doi=10.1117/12.148585 |publisher=International Society for Optics and Photonics |pages=2–14 |editor1-last=Blouke |editor1-first=Morley M.|citeseerx=10.1.1.408.6558 |bibcode=1993SPIE.1900....2F |s2cid=10556755 }}</ref> This was the basis for the PPS.<ref name="Fossum2014"/>

The [[noise (electronics)|noise]] of photodiode arrays is sometimes a limitation to performance. It was not possible to [[semiconductor device fabrication|fabricate]] active pixel sensors with a practical pixel size in the 1970s, due to limited [[microlithography]] technology at the time.<ref name=fossum93/>